Nowhere in the country have authorities done more to combat the spread of the laboratory-made drugs known as synthetic marijuana and bath salts than South Florida. But a Sun Sentinel investigation found that while poison control calls and drug arrests have dropped, the unprecedented community assault has yielded unsettling side effects — driving the illegal synthetic drug industry even further underground.

On the illicit market, clandestine chemists tinker with their compounds to stay one step ahead of the law, drug dealers ply the ever-evolving wares over the Internet to anyone with a credit card and a mailing address, and area youth know which convenience stores still sell the stuff under the counter.

In South Florida, where one of the nation's biggest manufacturers of synthetic marijuana built a bustling business in roadside warehouses, many teens and young adults are tripping out in ways surprising even to veteran emergency room doctors. And some are dying, destroyed by chemical concoctions doctors say have far worse effects on the mind and body than the marijuana and cocaine they are designed to mimic.

"The more recent products are the least known, and even more dangerous," said Jim Hall, director of the Center for the Study and Prevention of Substance Abuse at Nova Southeastern University in Davie. "People don't know what they're getting. Their favorite brands are changing from one week to the next."

According to poison control center statistics, synthetic marijuana has become especially appealing to South Florida youth. Its active ingredient, a chemical brewed in labs in China and India, was invented by an American chemistry professor to help the sick. Those who've tried it say it yields a disturbing, mind-addling high like few other drugs.

"One time, I was watching 'How I Met Your Mother' and I did it, and I had the loudest ringing in my ears," said Sam Hathaway, 17, of Pembroke Pines. "I couldn't understand anything going on on that show ... you get really confused."

Despite those dangerous effects, some former users know where to find it when they want it.

Max Earney, 17, of Cooper City, said all he would have to do is ask for "spice" — synthetic marijuana's street name — and the clerk at one store he knows will pull out a hidden box and sell him the latest brands.

"They don't even ask for ID," said Earney, one of several Broward County youths who spoke to the Sun Sentinel about their former drug use. "But they'll only sell it to you if they trust you."

Others do sell to strangers.

Even after bans made illegal the sale of anything resembling synthetic marijuana and its cocaine-like sister, bath salts, in Broward and Palm Beach counties last year, the Sun Sentinel recently was able to purchase three packets of brightly packaged "herbal potpourri" after requesting "legal marijuana" from the clerk at a Pompano Beach convenience store. At least one contained a compound that authorities say is illegal under federal law.

At a cost of $15.99 for three or four grams, the products appear to be packaged to appeal to youth. They sport eye-catching graphics and punchy brand names: Dead Man Walking, Joker and Cali Comfort.

Javier Yzquierdo, another former user, said he is particularly familiar with the Joker brand.

"I smoked three bowls of Joker one time, and I felt like my heart was beating out of my chest," said the Miramar 17-year-old.

The Sun Sentinel paid a private chemical laboratory, Toxicology Testing Services Inc. in Miami, to analyze the contents of the Dead Man Walking packet. It tested positive for UR-144, a synthetic cannabinoid, a chemical compound whose effects on receptors in the brain mimic a marijuana high — only at far more potent levels.

In court papers, the federal government calls UR-144 "a Schedule 1 controlled substance analogue" outlawed by the Controlled Substance Act. That same compound is at the heart of the feds' case against the West Palm Beach manufacturers of Mr. Nice Guy, one of the nation's top-selling brands of synthetic marijuana.

Violating the federal act can bring a prison sentence of five to 40 years. Florida law also now makes it a third-degree felony — punishable by up to five years in prison and a $5,000 fine — to sell, manufacture or deliver, or possess with intent to sell, advertise or deliver synthetic drugs.

"Our biggest problem to start with was this stuff was easier to buy than bubble gum," said Palm Beach County Sheriff Ric Bradshaw. "It was in the gas stations, the convenience stores. The proliferation was unbelievable.